Modeling and enhanced control of DFIG under unbalanced grid voltage conditions

This paper presents a mathematical model of a doubly fed induction generator (DFIG) based on stator voltage orientation (SVO) in the positive and negative synchronous reference frames under unbalanced grid voltage conditions. The oscillations of the DFIG electromagnetic torque and the stator active and reactive powers are fully described during grid voltage unbalance. A new rotor current controller implemented in the positive synchronous reference frame is proposed. The controller consists of a proportional integral (PI) regulator and a harmonic resonant (R) compensator tuned at twice the grid frequency. Thus, the positive and negative sequence components of DFIG rotor currents are directly regulated by the PI + R controller without the need of involving positive and negative sequence decomposition, which indeed improves the dynamic performance of DFIG-based wind power generation system during small steady-state and relatively larger transient network unbalances. The theoretical analysis and the feasibility of the proposed unbalanced control scheme are validated by simulation studies on a 1.5-MW wind-turbine driven DFIG system. Compared with conventional single PI current control design, the proposed control scheme results in significant elimination of either DFIG power or torque oscillation under unbalanced grid voltage conditions.     

Estimation of transmission line parameters from measurements

This paper describes the method of estimating the transmission line parameters from voltage, current, and power measurements at the two ends of the line. This becomes necessary if a new parallel transmission line is constructed between two substations due to load growth or if an underground cable replaces an overhead line and the overall parameters of the paralleled lines or the cable are desired to be determined. The parameters of the equivalent pi network of the line are obtained from the measurements at the line ends by using the Newton–Raphson method to solve the non-linear equations. The proposed method then gives the resistance/m, inductance/m, and capacitance/m, considering the distributed nature of the transmission line. The technique to determine the conductance parameter is also presented.     

基于CPLD的车载电子线束系统的设计

本文介绍了基于CPLD实现车载电子线束系统的设计方法,用于解决传统汽车布线多且复杂的问题.详细论述了整个系统的工作原理,主控和终端执行部分采用RS422标准形式进行通信,并在Altera公司的EPM7256S芯片上进行硬件设计和实时运行.软件部分使用VHDL语言和模块化的编程设计方法对CPLD进行设计,使系统具备了高性能、低功耗、工作温度范围宽、体积小和低成本等特点.最后采用Quartus II环境对程序进行仿真测试,结果证明该设计方案正确可行.     

金属带式汽车无级变速系统建模及动态仿真分析

无级变速(CVT)控制系统的难点是实现发动机和传动系统的最佳匹配。本文针对由发动机、离合器、CVT传动系统和汽车载荷构成的汽车整体模型,建立了无级变速汽车传动系统数学模型。在此基础上建立了以最佳燃油经济性为控制目的的整车动态仿真模型,设计了参数自调整PD速比控制器,并对4种典型汽车运行工况进行了仿真和分析。仿真结果表明所建模型正确合理。     

特高压直流输电系统实时闭环仿真建模

仿真研究是发展高压、超高压和特高压电网的必要手段。为深入研究特高压直流输电技术和特高压交直流混联系统的特性,基于RTDS仿真器和南瑞继保研制的±800kV直流控制保护样机搭建了云广直流输电系统"孤岛"运行方式实时闭环仿真模型。为验证所建模型的有效性和可信性,与非实时电磁暂态软件PSCAD/EMTDC对单电气元件特性、云广直流输电系统稳态潮流和暂态特征进行了仿真校核和分析。校核结果显示,2种仿真工具模拟的电气元件特性、系统稳态潮流和暂态特征基本一致,从而表明了搭建的实时闭环云广直流输电系统的可用性和可信性。由于考虑了UHVDC控制与保护设备的控制作用的实时参与,所搭建的闭环云广直流仿真系统将更能反映实际交直流系统的动态特性,更具实际工程参考价值。所述的闭环云广直流输电仿真系统已成功应用于云广特高压直流输电工程相关的多项关键科研项目,从而为云广特高压直流输电工程的建设和运行提供了有力的技术支持。     

Analysis of three-phase wound motors under unbalanced conditions

The analysis of three-phase wound motors with unbalanced supply voltages and unbalanced rotor-phase impedances is presented. The rotating field theory and coupling impedances approach are used in modelling the motor in the steady state. The effect of rotor skewing is considered. The relationships between stator and rotor quantities, in a general form, are obtained. The analysis is verified by comparison with the conventional equations for currents and torque.     

Characteristics of the magnetic field under hybrid ac/dc high voltage transmission lines

In recent years, the possibility for ac and dc transmission lines running parallel to each other, sharing the same right-of-way (ROW) or even the same-tower has increased. Design of such hybrid ac/dc networks requires a precise calculation of the magnetic field around and under them. This paper presents quantitative analysis of the magnetic field at 1-m height above ground surface for different hybrid ac/dc transmission lines. Lateral profiles for typical 275, 132 (running in Kuwait), 500, 220 and 132 kV (running in Egypt) ac transmission lines after adding bipolar dc lines are presented. The magnetic vector potential concept, as extended to multi-conductor transmission lines employing the superposition principle is used to model and calculate the RMS values of the magnetic field generated by the hybrid ac/dc lines at any point in the space. The RMS values of the field are determined directly without dividing the ac supply cycle into a sufficient number of subintervals.     

Wavelet transforms for real-time estimation of transmission line impedance under transient conditions

 Waveforms of voltages and currents in electrical power systems may include higher harmonics, transient components and random noise. For control and protection devices, it is necessary to estimate parameters of the basic waveform. The most well-known methods are based on the Fourier technique. The estimated phasors of the basic component can be applied to the calculation of the impedance of a faulty transmission line. In this paper, the current and voltage phasors were estimated using complex wavelets. The filter properties of the wavelet approach are better than those of the Fourier. Received: 20 July 2001/Accepted: 10 August 2001     

Watthour meter accuracy under controlled unbalanced harmonicvoltage and current conditions

This work presents the results of phase I of the project on the accuracy of watthour meters when subjected to closely-duplicated real-world unbalanced harmonic voltage and current conditions. Such real-world conditions involved differences in voltage and current magnitudes as well as differences in the voltage and current total harmonic distortion levels of each phase. Tests were performed on a selected sample of nine three-phase and three single-phase watthour meters. Some results showed that under a particular set of unbalanced waveforms with harmonic conditions of I_THD>80% and V_THD>2%, the percentage errors exhibited by these meters ranged from -10.09% to +0.52%     

输配电线路施工仿真培训系统的设计与实现

分析和使用了面向对象的软件设计和开发方法、Browser/Server网络结构体系,基于C#语言的平台技术,结合传统的仿真数学建模,设计了输配电线路施工仿真培训系统。介绍该系统的配置、功能、构成和特点,并且阐明该系统的设计思想和技术。该系统是集计算机、通信、多媒体的高新技术产物,系统采用Browser/Serve架构,符合当前计算机和网络的发展趋势。系统的设计突出了实用性、技术先进性和功能完备性,达到较高的应用水平。施工操作人员通过在该仿真培训系统上的演练,有利于快速掌握输配电线路施工的工艺流程,积累施工操作经验,对保证输配电线路施工的安全具有重要意义。     

Animations of electromagnetic transients in power transmission lines by means of the two-dimensional numerical Laplace transform

This paper presents the use of animations of the wave propagation phenomena on power transmission lines as a valuable tool for research and educational purposes. These animations are generated from data obtained by transient analysis in the frequency domain applying the two dimensional numerical Laplace transform. Since the line electrical parameters are defined in the frequency domain, the frequency dependence of such parameters is directly taken into account. These animations allow an insightful illustration of how travelling waves propagate along transmission lines during an electromagnetic transient, making them a useful tool to determine transient overvoltages that occur at internal points along power transmission lines. In the educational field, using these animations in electrical engineering courses can help students to have a better understanding of the traveling wave concept and how it differs from the circuit theory. In addition, it allows detailed comparison of the wave propagation along lines under different conditions, such as type of excitation, type of load, introduction of losses, etc.     

Establishing parameters of very high voltage power lines for various loadings and atmospheric conditions

The idea of establishing parameters of electro-power system elements under real conditions of work, and therefore of very high voltage power lines, was suggested at CIGRE congress of 1972. In Romania, I undertook the work on this applied research.In the classical theory of the symmetrical quadrupole of a very high voltage power line, it was considered known its uniform distributed parameters and the magnitudes of its input values and its output values unknown. The problem arising is to determine its internal parameters when the input and output values are known. It was necessary to develop an adequate mathematical method for this purpose, and in the first part of the article I present it in detail.The article presents an adequate way of measurement to reach this purpose, as well as the necessary cautions to do away with the possible errors of measurement, and a synthesis of the results obtained. It also presents one method for testing in laboratory, to double check the correctness of the results of the real high voltage line parameter measurements, because they seem to be abnormal, different from those previously considered as normal.The results of the measured parameters obtained in the laboratory model confirm the results obtained on the real high voltage lines. Finally, I present the theoretically explanation of this results.     

汽车用线缆的新发展

本文介绍随着汽车工业的现代化而对汽车内所用的电线电缆的改进。这些改进主要是用双金属线(铜包钢和铜包铝)来替代传统的铜导线;用新型的可交联聚酯弹性体来替代传统的绝缘材料。其主要目的在于减小线缆的尺寸和重量,增加了线缆的柔软性、耐热水性和耐热性等机械物理性能。文章描述了这些新产品的开发、性能试验和应用。     

Important parameters that influence crosstalk in multiconductor transmission lines

Transient surges in one of the overhead conductors, due to direct lightning strikes, causes crosstalk [C.R. Paul, Analysis of Multiconductor Transmission Lines, John Wiley & Sons, Inc., 1994; C.R. Paul, Introduction to Electromagnetic Compatibility, John Wiley & Sons, Inc., 1992] in other adjacent conductors. It is a common electromagnetic interference (EMI) phenomenon observed in power lines, communication lines and electrified railway lines. In this paper we investigate the crosstalk in multiconductor transmission lines (MTLs) above finitely conducting ground as a function of ground conductivity, heights of the receptor conductor and the terminal loads. For receptor conductor close to the ground, compared to the emitter conductor [C.R. Paul, Analysis of Multiconductor Transmission Lines, John Wiley & Sons, Inc., 1994; C.R. Paul, Introduction to Electromagnetic Compatibility, John Wiley & Sons, Inc., 1992], the decrease in ground conductivity increases the crosstalk peak currents at near end (end near to the source in the emitter conductor) of the receptor conductor, but at the far end it could either increase or decrease depending upon the line height and ground conductivity.     

特种绕组线的发展

本文简要的介绍了国内外最近绕组线 (包括纤维绕包线、薄膜绕包线、纸包组合及换位导线等 )及部分特种绕组线 (如无机绝缘电磁线、耐高温耐辐射电磁线、绞合电磁线、片状成型线圈等 )发展动态。另外 ,还介绍了绕包工艺及设备的最新进展     

Backflashover simulation of HV transmission lines with enhanced counterpoise groundings

This paper deals with the backflashover phenomenon in HV overhead transmission lines (TLs) with towers grounded by means of long counterpoises, typically used in high resistivity soils. Although long counterpoises are effective in reducing the grounding impedance at power frequency, their impulse response may affect negatively the TL backflashover rate. The study is focused on the enhancement of TL lightning performance obtainable by adding a small number of vertical grounding rods to horizontal counterpoises. An extensive ATP-EMTP parametric analysis, based on a detailed 161 kV TL model including the leader progression model (LPM) of line insulations and the non-linear transient behaviour of grounding systems, has been carried out taking into account several different values of soil resistivity as well as varying numbers, locations and lengths of additional vertical rods. Critical lightning current ranges causing backflashover have been then predicted for several lightning waveforms, of different severity. The paper shows that the addition of a few vertical grounding rods significantly improves TL lightning performance by increasing critical lightning current values, even if their influence is negligible at power frequency. The authors have ascertained an increment of average critical backflashover current up to ∼55% for some typical TL grounding system configurations and lightning waveshapes.     

Fault detection in transmission networks of power systems

An online fault detection scheme for a sample power system is introduced in this paper. The detection approach is based on the use of a variable structure system called “sliding mode observer”, where information contained in the output measurements is utilized to detect the onset of faults in the transmission network of the sample power system in real time and online. The power system comprises a generating unit connected to an infinite bus through double line transmission network. The common case of a fault occurring on a transmission line is illustrated through simulation studies.     

发电机励磁系统建模及仿真

励磁系统在电力系统的规划与控制领域都有非常重要的作用,精确的模型结构与参数是选择有效控制手段和整个电力系统仿真准确性的基础。通过小扰动试验校核了励磁控制系统小干扰动态特性和相关参数,为电力系统稳定分析计算提供了依据。     

地线绝缘的节能与载波通信的探讨

结合大量的光纤复合架空地线复合光缆(OPGW)工程设计实践,对于110~500 kV架空线路中的2条良导体地线,为了防雷逐塔接地所带来的电能损耗值得关注。如果能把良导体地线绝缘,节省的电能不可忽视,同时也给地线载波通信方式带来了生机。